Obama upbeat on Ukraine vote, but Russia's stance seen pivotal

* New Ukrainian leader seen having to move fast on promises (Recasts with Obama quotes, analyst comments, new throughout)

By Arshad Mohammed and Jeff Mason

WASHINGTON, May 25 (Reuters) - President Barack Obama suggested on Sunday that Ukraine's election may help unify the country, but analysts said that would depend largely on Moscow's influence and Kiev's ability to deal with daunting domestic challenges.

"The Ukrainian people have repeatedly demonstrated their desire to choose their leaders without interference and to live in a democracy where they can determine their own future free of violence and intimidation," Obama said in a clear allusion to Russian efforts to shape events in Ukraine.

"This election is another important step forward in the efforts of the Ukrainian government to unify the country and reach out to all of its citizens to ensure their concerns are addressed and aspirations met," he added, saying Ukrainians voted "even in parts of eastern Ukraine, where Russian-backed separatist groups sought to disenfranchise entire regions."

U.S.-based regional analysts voiced deep doubts that Russian President Vladimir Putin, having annexed Crimea in March and since pursued what the West regards as a policy of destabilizing eastern Ukraine, would reverse course.

They emphasized the scale of the economic and political problems that await billionaire Petro Poroshenko, who claimed Ukraine's presidency on Sunday after exit polls gave him more than 55 percent in a first round of voting.

A confectionery magnate with long experience in government, Poroshenko vowed to end the central government's conflict with pro-Russian rebels widely believed to be supported by Moscow and he pledged to align his country with Europe.

But it was Kiev's very movement toward Europe that is believed to have prompted Putin to annex Crimea and support pro-Russian separatists in the eastern provinces of Donetsk and Luhansk as a way of maintaining Moscow's influence.

After weeks of criticizing the Ukrainian election, Putin on Friday struck a conciliatory note. "We will treat the choice of the Ukrainian people with respect," he said. "After the election, we will work with the newly elected structure."

TAKING PUTIN WITH A GRAIN OF SALT

"I would take Mr. Putin's comments from Friday with a great deal of skepticism," said Steven Pifer, a former U.S. ambassador to Ukraine, who is now at the Brookings Institution think tank.

"If they respect the result and are prepared to deal with Poroshenko, it would be a major reversal of policy," he added.

Matthew Rojansky, director of the Woodrow Wilson Center's Kennan Institute, said it was "patently absurd" to expect Russia to suddenly abandon what it has long seen as a core national interest of preventing Ukraine from drawing closer to Europe.

Rojansky, who left Ukraine on Sunday after a visit to Kiev and Odessa, emphasized the scope of Ukraine's political and economic problems, many unaddressed for decades.

He said Poroshenko had the unenviable task of trying to satisfy the "Maidan" movement of pro-European protesters demanding deep political reform, while finding a modus vivendi with pro-Russian separatists, Ukraine's oligarch billionaires and Putin.

"He is stuck between a very massive immovable rock and a very big and very unpleasant wall," Rojansky said. "Those people are not going away and you cannot bludgeon them into submission."

Poroshenko will have to move fast to keep his campaign promises to clean up corruption and to move closer to Europe, said a Western diplomat who spoke on condition of anonymity.

"It's going to be a difficult, hard road to break the habits of the past," the diplomat said.

The United States and Europe will watch closely to see if Russia will work with Poroshenko and cut ties with pro-Russian separatists in Ukraine, the diplomat added, suggesting that otherwise, sanctions against entire sectors of the Russian economy may follow.

"If that does not happen, there will likely be more costs," the diplomat said. (Reporting by Jeff Mason and Arshad Mohammed; Writing by Arshad Mohammed; Editing by Bill Trott and Peter Cooney)

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